2018-04-19 02:48:35

by Marcos Paulo de Souza

Subject: [PATCH -next] user_namespace: Replace gotos with return statements

Found while inspecting the code that handles the setgroups procfs file.

Signed-off-by: Marcos Paulo de Souza <[email protected]>
---
Tested locally setting up a new userns, and setting setgroups as deny and allow,
worked as before.

kernel/user_namespace.c | 20 +++++++-------------
1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 246d4d4ce5c7..64a01254ac6b 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1142,22 +1142,18 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
struct user_namespace *ns = seq->private;
char kbuf[8], *pos;
bool setgroups_allowed;
- ssize_t ret;

/* Only allow a very narrow range of strings to be written */
- ret = -EINVAL;
if ((*ppos != 0) || (count >= sizeof(kbuf)))
- goto out;
+ return -EINVAL;

/* What was written? */
- ret = -EFAULT;
if (copy_from_user(kbuf, buf, count))
- goto out;
+ return -EFAULT;
kbuf[count] = '\0';
pos = kbuf;

/* What is being requested? */
- ret = -EINVAL;
if (strncmp(pos, "allow", 5) == 0) {
pos += 5;
setgroups_allowed = true;
@@ -1167,14 +1163,13 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
setgroups_allowed = false;
}
else
- goto out;
+ return -EINVAL;

/* Verify there is not trailing junk on the line */
pos = skip_spaces(pos);
if (*pos != '\0')
- goto out;
+ return -EINVAL;

- ret = -EPERM;
mutex_lock(&userns_state_mutex);
if (setgroups_allowed) {
/* Enabling setgroups after setgroups has been disabled
@@ -1194,12 +1189,11 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,

/* Report a successful write */
*ppos = count;
- ret = count;
-out:
- return ret;
+ return count;
+
out_unlock:
mutex_unlock(&userns_state_mutex);
- goto out;
+ return -EPERM;
}

bool userns_may_setgroups(const struct user_namespace *ns)
--
2.14.3

2018-04-19 03:46:16

by Eric W. Biederman

Subject: Re: [PATCH -next] user_namespace: Replace gotos with return statements

Marcos Paulo de Souza <[email protected]> writes:

> Found while inspecting the code that handles the setgroups procfs
> file.

What perchance might be the advantage of introducing multiple exits
into proc_setgroups_write?

I strongly suspect that if you look at the generated code it will
be worse after your patch.


Eric

> Signed-off-by: Marcos Paulo de Souza <[email protected]>
> ---
> Tested locally setting up a new userns, and setting setgroups as deny and allow,
> worked as before.
>
> kernel/user_namespace.c | 20 +++++++-------------
> 1 file changed, 7 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 246d4d4ce5c7..64a01254ac6b 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -1142,22 +1142,18 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
> struct user_namespace *ns = seq->private;
> char kbuf[8], *pos;
> bool setgroups_allowed;
> - ssize_t ret;
>
> /* Only allow a very narrow range of strings to be written */
> - ret = -EINVAL;
> if ((*ppos != 0) || (count >= sizeof(kbuf)))
> - goto out;
> + return -EINVAL;
>
> /* What was written? */
> - ret = -EFAULT;
> if (copy_from_user(kbuf, buf, count))
> - goto out;
> + return -EFAULT;
> kbuf[count] = '\0';
> pos = kbuf;
>
> /* What is being requested? */
> - ret = -EINVAL;
> if (strncmp(pos, "allow", 5) == 0) {
> pos += 5;
> setgroups_allowed = true;
> @@ -1167,14 +1163,13 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
> setgroups_allowed = false;
> }
> else
> - goto out;
> + return -EINVAL;
>
> /* Verify there is not trailing junk on the line */
> pos = skip_spaces(pos);
> if (*pos != '\0')
> - goto out;
> + return -EINVAL;
>
> - ret = -EPERM;
> mutex_lock(&userns_state_mutex);
> if (setgroups_allowed) {
> /* Enabling setgroups after setgroups has been disabled
> @@ -1194,12 +1189,11 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
>
> /* Report a successful write */
> *ppos = count;
> - ret = count;
> -out:
> - return ret;
> + return count;
> +
> out_unlock:
> mutex_unlock(&userns_state_mutex);
> - goto out;
> + return -EPERM;
> }
>
> bool userns_may_setgroups(const struct user_namespace *ns)

2018-05-02 14:13:43

by Christian Brauner

Subject: Re: [PATCH -next] user_namespace: Replace gotos with return statements

On Wed, Apr 18, 2018 at 11:46:38PM -0300, Marcos Paulo de Souza wrote:
> Found while inspecting the code that handles the setgroups procfs file.

This is not really improving anything so I unfortunately don't really
see why we should take this.

Christian

>
> Signed-off-by: Marcos Paulo de Souza <[email protected]>
> ---
> Tested locally setting up a new userns, and setting setgroups as deny and allow,
> worked as before.
>
> kernel/user_namespace.c | 20 +++++++-------------
> 1 file changed, 7 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 246d4d4ce5c7..64a01254ac6b 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -1142,22 +1142,18 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
> struct user_namespace *ns = seq->private;
> char kbuf[8], *pos;
> bool setgroups_allowed;
> - ssize_t ret;
>
> /* Only allow a very narrow range of strings to be written */
> - ret = -EINVAL;
> if ((*ppos != 0) || (count >= sizeof(kbuf)))
> - goto out;
> + return -EINVAL;
>
> /* What was written? */
> - ret = -EFAULT;
> if (copy_from_user(kbuf, buf, count))
> - goto out;
> + return -EFAULT;
> kbuf[count] = '\0';
> pos = kbuf;
>
> /* What is being requested? */
> - ret = -EINVAL;
> if (strncmp(pos, "allow", 5) == 0) {
> pos += 5;
> setgroups_allowed = true;
> @@ -1167,14 +1163,13 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
> setgroups_allowed = false;
> }
> else
> - goto out;
> + return -EINVAL;
>
> /* Verify there is not trailing junk on the line */
> pos = skip_spaces(pos);
> if (*pos != '\0')
> - goto out;
> + return -EINVAL;
>
> - ret = -EPERM;
> mutex_lock(&userns_state_mutex);
> if (setgroups_allowed) {
> /* Enabling setgroups after setgroups has been disabled
> @@ -1194,12 +1189,11 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
>
> /* Report a successful write */
> *ppos = count;
> - ret = count;
> -out:
> - return ret;
> + return count;
> +
> out_unlock:
> mutex_unlock(&userns_state_mutex);
> - goto out;
> + return -EPERM;
> }
>
> bool userns_may_setgroups(const struct user_namespace *ns)
> --
> 2.14.3
>

2018-05-04 01:24:07

by Marcos Paulo de Souza

Subject: Re: [PATCH -next] user_namespace: Replace gotos with return statements

On Wed, May 02, 2018 at 04:12:18PM +0200, Christian Brauner wrote:
> On Wed, Apr 18, 2018 at 11:46:38PM -0300, Marcos Paulo de Souza wrote:
> > Found while inspecting the code that handles the setgroups procfs file.
>
> This is not really improving anything so I unfortunately don't really
> see why we should take this.

Sorry for the late reply. My idea was to make the code more straightforward,
never happened to me this would led to a worse code being generated. So, please
discard the patch.

Thanks,

>
> Christian
>
> >
> > Signed-off-by: Marcos Paulo de Souza <[email protected]>
> > ---
> > Tested locally setting up a new userns, and setting setgroups as deny and allow,
> > worked as before.
> >
> > kernel/user_namespace.c | 20 +++++++-------------
> > 1 file changed, 7 insertions(+), 13 deletions(-)
> >
> > diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> > index 246d4d4ce5c7..64a01254ac6b 100644
> > --- a/kernel/user_namespace.c
> > +++ b/kernel/user_namespace.c
> > @@ -1142,22 +1142,18 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
> > struct user_namespace *ns = seq->private;
> > char kbuf[8], *pos;
> > bool setgroups_allowed;
> > - ssize_t ret;
> >
> > /* Only allow a very narrow range of strings to be written */
> > - ret = -EINVAL;
> > if ((*ppos != 0) || (count >= sizeof(kbuf)))
> > - goto out;
> > + return -EINVAL;
> >
> > /* What was written? */
> > - ret = -EFAULT;
> > if (copy_from_user(kbuf, buf, count))
> > - goto out;
> > + return -EFAULT;
> > kbuf[count] = '\0';
> > pos = kbuf;
> >
> > /* What is being requested? */
> > - ret = -EINVAL;
> > if (strncmp(pos, "allow", 5) == 0) {
> > pos += 5;
> > setgroups_allowed = true;
> > @@ -1167,14 +1163,13 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
> > setgroups_allowed = false;
> > }
> > else
> > - goto out;
> > + return -EINVAL;
> >
> > /* Verify there is not trailing junk on the line */
> > pos = skip_spaces(pos);
> > if (*pos != '\0')
> > - goto out;
> > + return -EINVAL;
> >
> > - ret = -EPERM;
> > mutex_lock(&userns_state_mutex);
> > if (setgroups_allowed) {
> > /* Enabling setgroups after setgroups has been disabled
> > @@ -1194,12 +1189,11 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
> >
> > /* Report a successful write */
> > *ppos = count;
> > - ret = count;
> > -out:
> > - return ret;
> > + return count;
> > +
> > out_unlock:
> > mutex_unlock(&userns_state_mutex);
> > - goto out;
> > + return -EPERM;
> > }
> >
> > bool userns_may_setgroups(const struct user_namespace *ns)
> > --
> > 2.14.3
> >

--
Thanks,
Marcos